In recent years, reactive oxygen metabolites have been postulated to be important mediators of immune-mediated, toxic and ischemic renal injury. See Paller, M. S. et al., Clin. Invest., 74:1156-1164 (1984); Shah, S. V. Kidney Int., 35:1093-1106 (1989); Stratta, P. et al., Contrib. Nephrol., 77:132-141 (1990); Stratta, P. et al., Am. J. Kid. Dis. 17:33-37 (1991); Guidet, B. et al., Am. J. Physiol., 257:F440-F445 (1989). They also are thought to play a role in endotoxin-induced tissue injury (Demling, R. H. et al., Arch. Surg., 123:1337-1341 (1988)), such as sepsis, as well as in reperfusion injury of heart and brain.
With respect to renal injury, investigators have determined that various antioxidants and free-radical scavengers appear to retard these injuries. Dietary deficiencies of the antioxidants selenium and vitamin E have been shown to greatly aggravate ischemic renal injury See Modi, K. S. et al., Kidney Int., 38:843-850 (1990). Others investigators have shown that probucol, an antioxidant, improves renal function following a release of bilateral ureteral obstruction (Modi, K. S. et al., Kidney Int., 38:843-850 (1990)) and that dimethylthiourea, a hydroxy radical scavenger, reduces proteinuria and renal histopathology in rats with immune complex glomerulonephritis. See Omata, M. Nippon Jinzo Gakkai Shi, 32:949-958 (1990).
With respect to the endotoxin-induced tissue injury resulting from sepsis, alpha-tocopherol and other scavengers have been shown to improve survival in rats. See Powell, R. J. et al., Am. Surg., 57:86-88 (1991). In these models, sepsis was induced by cecal ligation and puncture.
Other investigators have shown that reperfusion injury in rat heart can be greatly reduced by addition of pyruvate prior to ischemia. Studies have determined that pyruvate is a free-radical scavenger and can reduce H.sub.2 O.sub.2 generation by glucose oxidase. Investigators believe that pyruvate acts either through its direct reaction with H.sub.2 O.sub.2 or by activation of NADPH-dependent peroxide scavenging systems. See Cavallini, L. et al., J. Mol. Cell Cardiol., 22:143-154 (1990).
Various research groups have investigated the role of pyruvate in renal injury treatment. Pyruvate has been found to protect renal LLC-PK cells from peroxide-induced injury. See Salahudeen, A. K. et al., J. Am. Soc. Neph., 1:618 (1990) and Nath, K. A. et al., J. Am. Soc. Neph., 1:637 (1991). Others have determined that pyruvate infusion attenuates markedly the proteinuria caused by intrarenal infusion of H.sub.2 O.sub.2 and also reduces post-ischemic renal injury. See Cavallini, L. et al. J. Mol. Cell Cardiol., 22:143-154 (1990). Pyruvate is a naturally occurring 2-ketoacid and other similar compounds such as 2-ketobutyrate, 2-ketoglutarate, and 2-ketoadipate have been demonstrated to provide complete protection, at 1 mM, of Chinese Hamster V79 cells against the lethal effects of H.sub.2 O.sub.2. See Andrae, U. et al., Ziegler-Skylakakis K. Toxicology Letters, 28:93-98 (1985).
Arteriosclerosis is another example of a condition in which oxygen free-radical-mediated injury is believed to play a pathogenetic role. Circulating lipids, when oxidized by free radicals, become prone to deposition in the intimal lining of blood vessels, causing arteriosclerosis.
Free radical scavenging compounds have also been found to be protective in experimental models of acute pancreatitis and in a few patients with this disorder. Lipid peroxide levels are also elevated in this condition.
In patients with respiratory distress syndrome, reactive oxygen species may play a role, since increased concentrations of hydrogen peroxide are seen in expired condensate in such patients. Furthermore, plasma antioxidant activity is reduced.
Despite the demonstrated role of pyruvate as a free radical scavenger and its effects on reduction of reperfusion and renal injury, this compound is unlikely to be practical for use in actual treatment. It is known that pyruvate is relatively rapidly metabolized after its uptake. See Shreeve, W. W. et al., Acta. Endo., 65:155-169 (1970); Hartl, W. H. et al., Beitr. Infusionther., 25:389-398 (1990); Benevenga, N. J. et al., J. Dairy Sci., 47:1124-1126 (1965). Moreover, formulations containing pyruvate are usually not practical from a manufacturing and distribution viewpoint because the compound is too unstable. Similar limitations are applicable to the other naturally occurring 2-ketoacids discussed above.
In addition, the long-term toxicity of 2-ketobutyrate and 2-ketoadipate is unknown. Although 2-ketoglutarate, known to be non-toxic, may be useful as an antioxidant, it is known to be less effective than its monocarboxylic acid.
In addition to the problems of efficacy, unknown toxicity and stability discussed above, many antioxidants suffer from the problem that, after combining with oxygen free radicals and thereby becoming oxidized, they accumulate and can in turn promote oxidation of target molecules. Thus, there exists a need for treatments utilizing therapeutic compositions which can slow or stop the progression of disorders characterized by free-radical-mediated injury such as renal tissue injury, sepsis, reperfusion injury, arteriosclerosis, acute pancreatitis, or respiratory distress syndrome. Development of appropriate methods of treatment could lead to slowing or stopping of the progression of chronic renal failure and other disorders characterized by free-radical-mediated injury in animals and humans.